This invention relates generally to active array RF systems and more particularly to a receiver capable of simultaneously receiving N independent RF input signals, which can respectively have different, scan angles and be circularly or linearly, polarized.
The prior art describes various active array RF systems useful in a wide range of military and commercial applications for handling circularly and/or linearly polarized signals. For example only, U.S. Pat. No. 6,020,848 describes a phased array antenna system that allows reception of electrically selectable single polarity or simultaneous dual polarity/dual beam signals.
The present invention is directed to a wideband receiver system capable of simultaneously receiving multiple independent polarized (linearly or circularly) RF input signals from multiple sources within a wide scan angle range. Embodiments of the invention are suitable for a wide range of military and commercial application. The exemplary embodiment described herein is particularly suited for receiving input signals within the X/Ku band, e.g., between 10.9 and 15.35 Ghz.
A preferred receiver in accordance with the invention utilizes first and second linear orthogonal radiators for respectively receiving composite signals RFX and RFY. Each of the composite signals can contain multiple independent RF input signals, e.g., F1 at a frequency of f1, F2 at a frequency of f2, . . . FN at frequency fN. The composite signals, RFX and RFY, are respectively divided into multiple components, e.g., (where N=4) RFX1, RFX2, RFX3, RFX4 and RFY1, RFY2, RFY3, RFY4. The RFX and RFY components are then uniquely paired and processed in a polarization compensation stage by selective phase shifting based on the known polarization (e.g., left hand circular, right hand circular, linear 0-90xc2x0/180xc2x0-270xc2x0, and linear 90xc2x0-180xc2x0/270xc2x0-360xc2x0) of the signals to be received to produce four coherent signals, i.e., RFXY1, RFXY2, RFXY3, RFXY4. These four coherent signals are then selectively phase shifted in a scan angle compensation stage to recover the input signals F1, F2, F3, F4. The recovered input signals are then preferably band pass filtered.
More particularly, in a preferred embodiment, the composite signal RFX is applied to a four way divider which produces the four signals components RFX1, RFX2, RFX3, RFX4. Similarly, the composite signal RFY is applied to a four way divider to produce the signal components RFY1, RFY2, RFY3, RFY4. Each signal component contains contributions from the four input signals F1, F2, F3, F4. The RFX signal components are then respectively passed through controllable 90xc2x0 phase shift branches and the RFY signal components are respectively passed through controllable 180xc2x0 phase shift branches. The output of each 90xc2x0 phase shift branch is uniquely paired with an output from a 180xc2x0 phase shift branch and then summed in one of four two-way combiners to produce a coherent output. The 90xc2x0 and 180xc2x0 phase shift branches are digitally controlled to define a desired polarization angle, i.e., right hand circularly polarized, left hand circularly polarized, or linearly polarized, for each branch pairing. The following table describes an exemplary two bit control of the polarization phase shifters for each branch pairing for each polarity condition:
The coherent outputs of the four two-way combiners, each containing the input signals F1, F2, F3, F4, are then respectively applied to four digitally controlled phase shifters to compensate for scan angle. More particularly, the output of the first two-way combiner processing signals RFX1 and RFY1 is applied to a first phase shifter which is digitally controlled to define the scan angle of the input signal F1. Similarly, the outputs of the second, third and fourth two-way combiners are respectively applied to the second, third and fourth phase shifters which are respectively digitally controlled to define the scan angles of signals F2, F3, F4. The outputs from the scan angle phase shifters, which comprise the received input signals F1, F2, F3, F4, are then preferably passed through band filters respectively tuned to f1, f2, f3, f4. A preferred implementation of a receiver in accordance with the invention utilizes multiple substrates configured for stacking into a compact substrate assembly. The preferred substrate assembly includes six substrates or layers configured as follows:
Layer 1=Radiator/Balun Substrate
Layer 2=Low Noise Amplifier (LNA) Substrate
Layer 3=First Circular/Linear Polarization Control Substrate
Layer 4=Second Circular/Linear Polarization Control Substrate
Layer 5=Scan Control Substrate
Layer 6=Regulator Substrate
The substrates are connected vertically preferably using fuzz-button interconnects, and caged via hole technology.
The preferred substrate assembly comprises a sixteen channel device. That is the Radiator/Balun substrate forms a sixteen element matrix in which each element contains orthogonally polarized radiators for supplying composite signals RFX and RFY. Each element is coupled through the layers of the stack assembly forming the aforedisccussed receiver to recover four input signals F1, F2, F3, F4